The technical field of this invention is corneal surgery and, in particular, the invention relates to methods and pharmaceutical compositions for treating the cornea following laser reprofiling operations.
Various surgical techniques are known for altering the surface of the cornea to correct refractive errors in vision. Such techniques include radial keratotomy ("RK") in which a set of radial incisions, i.e., resembling the spokes of a wheel, are made in the eye, down into the stroma of the cornea. As the incisions heal, the curvature of the eye is flattened, thereby remedying myopic conditions. Additionally, operations, such as keratoplasty, have been performed in which the surface of the cornea is sculpted to a new desired shape.
Until recently, such surgical operations on the cornea were most commonly carried out using diamond or steel knives or razors. However, corneal surgery, particularly with mechanical instruments, has often been less than satisfactory because the basement membrane upon which the epithelium attaches to the corneal proper is destroyed or damaged to an extend where epithelial cells cannot regrow and form a continuous protective layer over the surface of the eye.
Recently, new laser surgical techniques have been developed to ablate or otherwise treat corneal defects without mechanical abrasion. These techniques include photorefractive keratectomy ("PRK") and phototherapeutic keratectomy ("PTK") in which laser radiation is applied to the cornea with minimal heating effects to ablate or smooth refractive aberrations. Such laser techniques will usually create a pseudo basement membrane (or smooth anterior surface) on the outside of the cornea which facilitates epithelial cell attachment and, hence, healing of the eye.
Nonetheless, even with laser surgical approaches, there exists a need for methods and agents to facilitate corneal healing.
A new technique for corneal reshaping involves the use of a pulsed laser photoablation apparatus to ablate very thin layers of corneal tissue with greater precision than can typically be achieved with mechanical means. Such laser photoablation procedures typically employ a beam shaping or masking apparatus which varies the size of the exposure area on the corneal surface over time or provides a predefined profile of resistance to the laser radiation, such that areas of the cornea receive different cumulative exposures and thereby are ablated to varying depths.
These laser corneal reprofiling operations are typically referred to as photorefractive keratectomy ("PRK") and are performed with a high energy excimer laser which emits ultraviolet ("UV") laser radiation which is capable of ablating biological tissues without thermal damage to surrounding tissue. For further details on PRK techniques, see Marshall et al, "Photo-ablative Reprofiling Of The Cornea Using An Excimer Laser: Photorefractive Keratectomy," cit. Vol. I, Lasers in Ophthalmology, pp. 21-48 (1986) and U.S. Pat. Nos. 4,856,513 and 4,941,093.
In clinical trials of PRK procedures, patients typically experience some ocular discomfort immediately following surgery, together with a "cloudiness" in vision, which usually resolves itself in a matter of days or weeks.
There exists a need for methods for treating the newly reprofiled surface of the cornea to minimize the discomfort and visual artifacts that often accompany PRK procedures. In particular, compositions which can be topically applied to the eye in order to reduce discomfort and/or visual artifacts would satisfy an important medical need.